Telephone system.



E. R. NUM B. c. enoH.

Patented Feb. 19, 1918.

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Y@ 9% e QM@ EARL R. NEIR, OF CHICAGO, ILLINOIS, AND BERNARD C. GROH, OFST. PAUL, MINNESOTA,

AssIGNoRs To AUTOMATIC nA'rIoN or ILLINOIS.

ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPO- TELEPHONE SYSTEM.

Specification of Letters Patent.

Fatented Feb. i9, 1918.

Application led March 20,1916. l Serial No. 85,435.

have invented certain new and useful Im-v provements in TelephoneSystems, the following isa specification. p K Cur invention relates totelephone systemsI and has particular reference to such systems ascomprise a plurality of widely separated exchanges interconnected bytoll lines.

In the systemy of the above general character certain exchanges may beinterconnected through the medium of toll lines which terminate in athird intermediate exchange. It

of which is customary where the intermediate ex.

change is of considerable size to terminate the toll lines in a tollboard centrally'located as regards the local subscribers; and, incompliance with the dictates of modern practice, that portion of thetoll lines which lies within the city proper is usually composed ofcable. y

To avoid the inclusion of the cable in through connections a so calledswitching station may beprovided, located at the outskirts of the cityat the point where the open wire lines are joined to the cableconductors extending to the toll board. Operators at the switchingstation are provided with means for directly connecting any two openwire toll lines in response to orders transmitted from the toll board.

The principal object of o-ur invention is to provide, at the tollswitching station of an intermediate exchange` means comprisingautomatic switches and controlling circuits therefor whereby theoperators stationed at the toll board may control the interconnection oftoll lines without the intervention of lother operators.

Further objects of our invention relate to details o-f circuitarrangement whereby well known types of automat-ic switches may be usedin conjunction with well known manual apparatus to form a complete andefficient automatic toll switching system.

Having given a general statement of the object and scope of ourinvention, now proceed to a description of the operation of the same,reference being had to the accompanying drawings. in which Figure 1represents diagrammatically the layout ofl we will the telephone systemdisclosed herein, and Fig. 2 represents a complete circuit connectionbetween a toll line indicated by reference characters 52 and 53 and. asecond toll line indicated similarly by reference characters 50 and 51;together with certain manual equipment to be descriled hereinafter. Theaforesaid connection has been established through the medium of theautomatic switches H and H and the cut-off relays 4 and 24, as willappear more clearly hereafter.

Referring now to Fig. 1, A and represent exchanges at outlying townswhich are connected with the intermediate exchange in the city C throughthe medium of toll lines t. It will be seen that these toll lines passthrough the switching station S before entering the toll board T in theintermediate exchange. In general our improved system contemplates theprovision of automatic switches at the switching station S connected inpairs and controllable by operators stationed at the toll board T. Anoperator at the exchange A who desires to obtain connection Lith theexchange B will signal the operator at the intermediate exchange in thecity C in the regular manner, the signal ap-I pearing on the toll boardT. The operator at exchange C. upon learning the connection desired,will signal the operator at exchange B, and will then proceed to connectthe toll lines to the respective exchanges A and B directly, through themedium of a pair of automat-ic switches at the switching station S.Circuits are provided whereby the toll operator at exchange C cansupervise the connection and terminate it at will -by disconnecting theautomatic switches.

Referring now to Fig; `2the -toll lines 52-53 and 50-51, which may beassumed to extend, respectively, to the exchanges A and B (Fig. l), areprovided at the toll board in the intermediate exchange with the regularmultiple jacks and drops shown at and M', tol which they are normallyconnected through back contacts-of relays 4 and Q4, respectively. one ofwhich is shown at L, which may be used to connect two toll lines bymeans of their multiple jacks, but which are ordinarily used only fo-ranswering, signaling and supervising. ,A

The cord circuit L may be of any well known or suitable type. As hereinrepresented it consists essentially of the plugs P and Pv connected bythe two strands of the cord with a signal 2 in bridge thereof.` Alistening key K is provided by means of which the operator is enabled toconnect her head set with the' cord circuit at the proper time, and aringing key K affords means for projecting ringing current from thegenerator R` ont over a called toll line.

The automatic switches H and H are, of the general type of connectorlswitch disclosed in U. S. Letters Patent #815.176, granted Mai-ch 13,and Erickson; the circuits being modified, however, to enable theswitches to operate iii accordance with the principles of our invention.Considering lirst the connector H, it comprises among other details abank of contacts arranged in horizontal rows or levels, which contactsare adapted to be engaged by a set of wipers 5, 6, and 7 carried upon ashaft (not shown) which has a vertical movement controlled by thevertical magnet 8 and a rotary movement controlled by the rotary magnet9. The usual side switch comprising the wipers 10 and 11 is controlledby the private magnet 12 in the well known manner. Means for permittingthe switch to be restored to normal position is provided in the releasemagnet 14 which, upon energizing, withdraws the retaining pawls from theshaft and returns the side switch wipers to their irst position. Thecontact 15 makes against its spring only when the shaft has been raisedone or more steps from its normal position. The relays 16 and 17 areslow acting. The operation of the various parts ot' the switch iscontrolled' through the medium of the line relay 13.

The connector H is almost identical with connectorvH in constructionexcept that it has no line relay, being controlled by the line relay 13after the connector H has been operated.

It will be observed that the wipers 105 and 107 of the connector H arenormally connected directly with the wipers 5 and 7 of the connector H,the combination of the two sets of wipers and their connectingconductors forming a link circuit. The bank contacts to which these setsof wipers have access t'cim terminals of the toll lines entering theswitching station. each toll line having a set of multiple bank contactsaccessible to each connector. These bank contacts of course are alsomultipled in the banks of as many other connector pairs as arenecessary7 to handle the trathc. y i

Each toll line is provided, tioned, with a cut-ofi' relay, one of whichis indicated by reference character 4, which serves to disconnect itsassociated toll line from the apparatus at the toll board and to connectit with its multiple contacts in the banks of the connector switches.The cutas before men- 1906, to Keith, Erickson,l

. will oil' relays are controlled over the private wipers of theconnector switches.

The upper conductor of the link circuit shown in Fig. 2 is connected byway of impedance coil 36, condenser 56, cable conductor 73. andcondenser with one strand of the cord circuit L. The lower conductor isconnected by way of impedance coil 35, condenser 57, cable conductor 72,and condenser 71 with the other strand of the cord circuit L. The drop1signal 2 and the impedance coil I8 are bridged across the conductors 72and 73, the former at the toll board and the latter at the switchingstation. Through the medium of the double windings of the drop 2 and theimpedance coil 48 av simplex circuit is superimposed on the conductors72 and 7 3 to form a controlling circuit for the automatic switches Hand H. The keys K2 and K3 are individual to the cord circuitL and itsassociated link circuit, vand there are as many sets of keys similar tokeys K2 and K3 as there are cord circuits. Any key K2, when operated,serves to complete the simplex controlling circuit for the automaticswitches of its associated link circuit at the switching station. whilethe corresponding key K3, when operated serves to insert a callingdevice D in the cuit.

The calling device D, represented herein by a pair of impulse springs18, may be of any well known or suitable type, such, t'or` example, asis shown in British Patent to S. G. S. Dicker, #29,654 of 1910. .Acalling device of the above type consists essentially of a pair ofimpulse springs which may be separated a variable number of timesthrough the medium of an impulse wheel controlled by a finger hole dial.

For supplying current for operating purposes we have shown twobatteries, indicated by reference characters B and B', each having'oneterminal grounded. For supplying ringing current we have shown a ringingcurrent generator, indicated by reference character R.

Having given a general description of the.

aforesaid controlling cirapparatus employed in our invention, we

now proceed to an explanation of the operation of the` same. Inasinuchas a great deal ofthe apparatus shown herein is old and well known iiithe art, having been fully described in the publications hereinbet'oi'ei'ekferred to, the operation will be described in a more or less generalmanner, the details being given only where they have to do in somerespect with the application of the principles of our invention. For thepurposes ot' this explanation it will be assumed that an operator atexchange A (Fig. 1) wishes to connect with an operator at exchange B. Toestablish such a connection the services of an operator at intermediateexchange C are required. Accordingly,vthe operator at cx- Lef-eserchange A inserts a plug in the multiple jack of a toll line extending tothe intermediate exchange C, assumed in this case to be the toll line52-53 (Fig. 2), and then projects ringing current over the toll line bymeans of her ringing key, all in the well known manner.

In response to the operation of the ringing key by the operator atexchange A, the drop 3 on the toll board at the exchange C is actuated,thereby notifying the operator stationed at the toll board of the call.Upon perceiving the actuated drop, the operator may insert the plug P ofher cord circuit L in the multiple Jack J, thereby disconnecting thedrop 3 and energizing the magnets V which may be used to operatesuitable visual busy signals (not shown). The operator at exchange C maynow operate her listening Vkey K and converse with the operator atexchange A. Being informed that connection is desired with exchange B,the operator at exchange C may now insert plug P of her cord circuit Lin the multiple jack J2 of a t-oll line extending to exchange B, assumedin this case to be toll line 50-51- As a result of the insertion of theplug in jack J 2, the drop 103 is disconnected and the associatedvvisual busy signalsl (not shown) controlled by the magnets V areactuated. The ringing key K may now be operated to project ringingcurrent over toll line 50-51 to signal the operator at exchange B.

The operator at exchange C may now proceed to connect the two toll lines52-53 and 50 51 directly, by means of the connector switches H and H atthe switching station. It is understood that each toll line terminatingat the toll board at exchange C is assigned a two digit numbercorresponding to the position of the contacts of that line in the banksof the connectors at the switching station. Also since all connectorshave access to all toll lines it is immaterial which. number is calledfirst.

To proceed with the operation, by throwing key K2 a circuit is completedfor the line relay 13 which may be traced as follows: ground at G,winding of relay 13, windings of retardation coil 48 in parallel.conductors 72 and 73 in parallel, windings of drop 2 in parallel,contact springs 81 and 82 of key K3, and contact springs 81 and S5 ofkey K2 to battery B. Upon energizing, relay 13 completes a circuit forslow acting relay 16 of connector H over the following path: ground atG2, contact springs 19 and 47, and winding of relay 16 to battery B.Relay 16, upon attracting its armature, opens a contact in the circuitof the release magnets 38 and 1l and prepares a circuit for the verticalmagnet 8 of connector H.

r1`he operator may now throw her key K3, thereby inserting the callingdevice D in the previously described circuit of relay 13 in an obviousmanner. The apparatus is'now in readiness for the operation of thecalling device D. By manipulating the finger hole dial in accordancewith the first digit of the number of toll line 50-51, the impulsesprings 18 are separated momentarily a number of times, resulting in acorresponding number of denergizations of relay 13. At

each denergization relay 13 sends an impulse to the vertical magnet 8over the following path: ground at G2, contact springs 19 and 20,contact springs 21 and 22, winding of slow acting relay 17, winding ofvertical magnet 8, and side switch wiper 10 in its first position tobattery 13. 1n response to these impulses the vertical magnet 8operates-to raise the shaft until the wipers 5, 6 and 7 stand oppositethe level in which are located contacts which are terminals of toll line:BO-51. Relay 17 is energized in series with the vertical magnet andbeing slow acting retains its armature attracted during the series ofimpulses. 1n its operated pose tion relay 17 disconnects the wipers 5and 7 and also completes an energizing circuit for the private magnet12. At the end of the series of impulses relay 17 retracts its armaturethereby breaking the private magnet circuit. The consequent energizationand denergization of the private magnet operates to advance the sideswitch wipers 10 and 11 to their second positions in the well knownmanner. It should be mentioned at this point that relay 16, being slowacting, does not respond to momentary denergizations of relay 13 butretains its armature in an operated position.

The calling device D may now be operated in accordance with the secondand final digit of the number of toll line 50-51, resulting as before indenergizations of relay 13. At this time, however, side switch wiper 10being in its second position, relay 13 sends impulses to the rotarymagnet 9` thereby rotating the wipers 5, 6. and 7 until they reach thebank contacts 91, 92, and 93 which are terminals of toll line 50-51.Relay 17 is also in series with the rotary magnet and responds to theseries of impulses therethrough to control the private magnet in themanner already described, whereby the side switch wipers 10 and 11 areadvanced to their third position.

An energizing circuit may now be traced for relay 2i over the followingpath: ground at G4, winding of relay 2-1, bank contact 92. wiper 6, andside switch wiper 10 in its third position to battery B. Upon attractingits armature, relay 24 disconnects the toll line 50-51 from the cableconductors 87-88 extending to the toll board and connects it to itsmultiple contacts in the connector banks. one set of these contactsbeing the set 91-93 upon which the wipers of connector H are nowresting.

As side switch wiper 11 comes onto its third position contact point acircuit is" completed for slow acting relay 25 of the connector H whichmay be traced as follows: ground at G2, contact springs 19 and 47, sideswitch wiper 11 in its third position, and winding of relay 25 tobattery B. Relay 25. upon energizing. prepares a circuit for thevertical magnet 28.

The operator may now operate her calling device D in accordance with thefirst digit of the number of the toll line S2-53. There follows asbefore a corresponding number of denergizations of the relay 13 whichnow sends impulses to the'vertical magnet 28 of the connector H over thefollowing path: ground at G2. contact springs 19-and 20, contact springs26, winding of rerelay 27, winding of vertical magnet 28, and sideswitch wiper 30 in its first position to battery B. In response to theseimpulses the vertical magnet 28 operates to raise the shaft of connectorH until the Wipers 105, 106, and 107 stand opposite the level in whichare located contacts which are terminals of the toll line 52-53. Relay25, being slow acting, remains energized during the interruptions of itscircuit by relay 13. Relay 27, energized in series with the verticalmagnet 28. performs the same function for connector H as'relay 17 did inthe case of connector H. In other words. relay 27 controls the privatemagnet 33 whereby the side switch wiper 30 is advanced to its secondposition at the end of the first series of impulses directed toconnector H. The calling device D may now be operated in accordance withthe second and final digit of the number of toll -line 52-53, resultingagain in de'efnergizations of relay 13. Side switch wiper 30 being inits second position, impulses are now sent through ythe rotary magnet 29which operates in response thereto to rotate the wipers 105, 106, 107until they arrive at bank contacts 94, 95. and 96 which contacts areterminals of toll line 52-53. Relay 27 again controls the private magnet33 to advance the side switch wiper 30 to its third position.

An energizing circuit for relay 4 may now be traced as follows: groundat G, Winding of relay 4, bank contact 95, wiper 106, and side switchwiper 30 to battery B.

Upon attracting its armature, relay 4 dis-- connects the toll line 52-53from the cable conductors 62-63 extending to the toll board and connectsit to its multiple contacts in the connector banks, one set of thesecontacts being the set 94-96, upon which the wipers of connector H arenow resting.

The required direct connection between the two toll lines has now beencompleted over the path shown in the heavy lines.

Having finished dialing the numbers required to set up the connectionjust described the operator may restore her key K3 thereby making thecalling deviceJ D accessible for use in establishing other connections.By throwing her listening key K the operator is enabled to observe theprogress of the conversation over the through connection, if necessary,by reason of the connection between the strands of her cord circuit andthe link circuit. The impedance coils 35 and 36, however, reduce theefficiency of this connection as regards the shunting of voice currentsfrom the connected toll lines, thereby preventing the operator atexchange C from seriously interfering with the through connection,although she can hear well enough to satisfy herself that it isprogressing satisfactorily.

When the conversation has been completed the operator at, exchange Awill operate her ringing key again to project ringing current over thetoll line, thereby actuating the drop 2 in bridge of the twov conductorsof the link circuit. Upon perceivmg the actuated drop the operator atexchange C is informed that disconnection is desired, whereupon she willremove plugs P and P from the jacks and restore key K2 to its normalposition. Upon restoring key K2 the circuit of relay 13 is broken.yRelay 13, upon denergizing, breaks the circuit of slow acting relays 16and 25. Relay 16, upon denergizing, completes a circuit for the' releasemagnet 14 of connector H and also for release magnet.

38 of connector H, whereupon the connectors are restored tonormalposition in the well known'manner. The release magnets 14 and 38'have their circuits broken at off normal contacts 15 and 31,respectively, when the connectors reach their normal position. When theside switch wipers 30 and 10 are restored to first position by therelease of the connectors the previously described energizing circuitsfor relays 4 and 24. are broken, whereby these relays are denergized andthe toll lines are again connected to their respective apparatus at thetoll board.

It will be seen fromthe foregoingthat we have provided a szmple andefficient automatic toll switching apparatus through .the medium ofwhich operators stationed at a toll board are enabled to accomplish thethrough switching of toll lines at a distant switching station, therebydispensing with the operators at the switching station.

While we have foundi convenient in explaining our invention toillustrate and describe a certain specific embodiment thereof, we do notwish to be held strictly to the exact form shown herein, for va- .riousadaptations will no doubt suggest themselves to -persons skilled in theart.

What we claim as our invention is:

1. In a trunking system, a pair of lines, an`

operators position, fixed termlnals for said lines normally disconnectedtherefrom, a link circuit, movable terminals at each end of said link,means operable for advancing one of said movable terminals intoengagement with the fixed terminal of either of said lines, and meansoperable for advancing the other of said movable terminals intoengagement with the fixed terminal of the other of said lines, and meanscontrolled solely by said operator for disengaging said movableterminals from said fixed terminals.

2. In a trunking system, a pair of lines, an operators position, fixedterminals for said lines normally disconnected therefrom, a linkcircuit, movable terminals at each end of said link, means operable foradvancing one of said movable terminals into engagement with the fixedterminal of either of said lines, means operable for advancing the otherof said movable terminals into engagement with the fixed terminal of theother of said lines and a relay for. each of said lines for connectingits associated fixed terminals, and means controlled solely by saidoperator for disengaging said movable terminals from said fixedterminals.

3. In a trunking system, a pair of lines, an operators position, fixedterminals for said lines normally disconnected therefrom, a linkcircuit, movable terminals at each end of said link, means operable foradvancing one of said movable terminals into engagement with the fixedterminal of either of said lines, and means operable for advancing theother of said movable terminals into engagement with the fixed terminalof the other of said lines, each of said means comprising an automaticswitch, and means controlled solely by said operator for releasing saidswitches.

4. In a trunking system, a pair of lines, an operators position, fixedterminals for said lines normally disconnected therefrom, a linkcircuit, movable terminals at each end of said link, means operable foradvancing one of said movable terminals into engagement with the fixedterminal of either of said lines, means operable for advancing the otherof said movable terminals into engagement with the fixed terminal of theother of said lines, each of said means comprising an automatic switch,and a relay for each of said lines for connecting its associated fixedand means controlled solely by said operator for releasing saidswitches.

5. In a trunking system, a pair of lines,

fixed Vterminals for ysaid lines normally disterminals,

connected therefrom, a link circuit, movable terminals at each end ofsaid link, means operable for advancing one of said movable terminalsinto engagement with the fixed terminal of either of said lines, andmeans operable for advancing the other of said movable terminals intoengagement with the fixed terminal of the other of said lines, each ofsaid v-means comprising an automatic switch, and a common controllingcircuit for said switches.

6. In a trunking system, a pair of lines. fixed terminals for said linesnormally disconnected therefrom, a link circuit, movable terminals ateach end of said link, means operable for advancing one of said movableterminals into engagement with the fixed terminal of either of saidlines, means operable for advancing the other of said movable terminalsinto engagement with the fixed terminal of the other of said lines, eachof said means comprising an automatic switch, a relay for each of saidlines for connecting its associated fixed terminals, and a commoncontrolling circuit for said switches.

7. In a trunking system, a pair of lines, fixed terminals for saidlines, a link circuit, movable terminals at each end of said link, meansoperable for advancing one of said movable terminals into engagementWith the fixed terminal of either of said lines, means operable foradvancing the other of said movable terminals into engagement with thefixed terminal of the other of said lines, each of said means comprisingan automatic switch, a common controlling circuit for said switchesnormally adapted to control a first one of said switches, and meansincluded in said first switch for shifting the control to the other ofsaid switches.

8. In a trunking system, a pair of lines, fixed terminals for said linesnormally disconnected therefrom, a link circuit, movable terminals ateach end of said link, means operable for advancing one of said movableterminals into engagement with the fixed terminal of either of saidlines, means operable for advancing the other of said movable terminalsinto engagement with the fixed terminal of the other of' said lines,

each of said means comprising an automatic switch, a common controllingcircuit for said switches normally adapted to control a first one ofsaid switches, and means included in said first switch for shifting thecontrol to the other of said switches.

9. In a trunking system, a pair of lines, fixed terminals for said linesnormally disconnected therefrom, a link circuit, movable terminals ateach end of said link, means operable for advancing one of said movableterminals into engagement with the xed terminal of either of said lines,means operable for advancing the other of said movable terminals intoengagement with the fixed terminal of the other of said lines, each ofsaid means comprising an automatic switch,

a relay for each of said lines for connecting its associated fixedterminals, a' common controllingcircuit for said switches normallyadapted to control a first one of said switches, and means included .insaid first switch for shifting the control to the other of saidswitches.

10. In a trunking system, a pair of lilies, fixed terminals for saidlines normally disconnected therefrom, a link circuit, movable terminalsat each end of said link, means operable for advancing one of saidmovable terminals into engagement with the fixed terminal of either ofsaidlines, means operable for advancing the other of said movableterminals into engagement with the fixed terminal of the other of saidlines, each of said means comprising an automatic switch, a relay foreach of said lines for connecting its associated fixed terminals, acommon controlling circuit for said switches normally adapted to controla first one of said switches. means included in said first switch forshifting the control to the other of said switches, and means in saidswitches for controlling said relays.

11. In a trunking system, a plurality of lines, an operators position,fixed terminals for each of said lines normally disconnected therefrom,a link circuit having movable terminals at each end, means operable foradvancing one of said movable terminals into engagement with a fixedterminal of any one of said lines, and means operable for also advancingthe other of said movable terminals into engagement with a fixedterminal of any one ofsaid lines, and means controlled solely by saidoperator for disengaging said movable terminals from said fixedterminals.

12. In a trunking system, a plurality of lines, an operators position,fixed terminals for each 0f said lines normally disconnected therefrom,a link circuit having movable terminals at each end. means operable foradvancing one of said movable terminals into engagement with a fixedterminal of any one of said lines, means operable for also advancing theother of said movable terminals into engagement with a fixed `terminalof any one of said lines, and a relay for each of said lines forconnecting its associated fixed terminals, and means controlled solelyby said operator for disengaging said movable terminals from said fixedterminals.

13. In a trunking system, a plurality of lines, an operators position,fixed terminals for cach of said lines normally disconnected therefrom,a link circuit having movable terminals at each end,vmeans operable foradvancing one of said operable terminals circuit for said switchesnormally into engagement with a fixed terminal of any one of said lines,and means operable for also advancing the other of said movableterminals into engagement with a fixed terminal of any one of saidlines, each of said means comprising an automatic switch, and meanscontrolled solely by said operator for releasing said switches. v

14. In a trunking system, a plurality of lines, an operators position,fixed terminals for each of said lines normally disconnected therefrom,a link circuit having movable terminals at each end, means operable foradvancing one of said movable terminals into engagement with a fixedterminal of any one ofl said lines, means operable for also advancingthe other of said movable terminals into engagement with a fixedterminal of any one of said lines, each of said means comprising anautomatic switch, and a relay for each of said lines for connecting itsassociated fixed terminals, and means controlled solely by said operatorfor releas-4 ing said switches.

l5. In a trunking system,'a plurality of lines, fixed terminals for eachof said lines normally disconnected therefrom, a link circuit havingn'iovable'terminals at each end, means operable for advancing one ofsaid movable terminals into engagement with a fixed terminal of any oneof said lines, means operable for also advancing the other of saidmovable terminals into engagement with a fixed terminal of any one ofsaid lines, each of said means comprising an automatic switch and acommon controlling circuit for said switches.

16. In a trunking system, a plurality of lines, fixed terminals for eachof said lines normally disconnected therefrom, a link circuit havingmovable terminals at each end, means operable for advancing one ofsaidmovable terminals into engagement with a fixed terminal of any one ofsaid lines. means operable for also advancing the other of said movableterminals into engagement with a fixed terminal of any one of saidlines, each of said means comprising an autcmatic switch, a relay foreach of said lines for connecting its associated and a commoncontrolling circuit for said switches.

17. In a trunking system, a plurality of lines, fixed terminals for eachof said lines, a link circuit having movable terminals at each end,means operable for advancing one of said movable terminals intoengagement with` a fixed terminal of any one of said hnes, meansoperable for also advancing the other of said movable terminals into engagement with a fixed terminal of any one 'of said lines, each of saidmeans comprising an automatic switch, a common controlling adapted tocontrol a first one of said switches, and

fixed terminals,

insane? means included in said first switch for shifting the control tothe other of said switches:

18.111 a trunking system, a plurality of lines, fixed terminals for eachof said lines normally disconnected therefrom, a link circuit havingmovable terminals at each end, means operable for advancing one of saidmovable terminals into engagement with a fixed terminal of any one ofsaid lines, means operable for also advancing the other of' said movableterminals into engagement with a fixed terminal of any one of saidlines, a common controlling circuit for said switches normally adaptedto control a first one of said switches,1 and means included in saidfirst switch for shifting the control to the other of said switches.

19. In a trunking system, a plurality of lines, fixed terminals for eachof said lines normally disconnected therefrom, a link circuit havingmovable terminals at each end, means operable for advancing one of saidmovable terminals into engagement with a fixed terminal of any one ofsaid lines, means operable for also advancing the other of said movableterminals into engagement with a fixed terminal of any one of saidlines, each of said means comprising an automatic switch, a relay foreach of said lines for connecting its associated fixed terminals, acommon controlling circuit for said switches normally adapted'to controla first one cf said switches, and means included in said first switchfor shifting the control to the other of said switches.

20. fna trunkingsystem, a plurality of lines, fixed terminals for eachof said lines normally disconnected therefrom, a link circuit havingmovable terminals at each end, means operable for advancing one of saidmovable terminals into engagement with a fixed terminal of any one ofsaid lines, means operable for also advancing the other of said movableterminals into engagement with a' fixed terminal of any one of saidlines, each ofl said means comprising an automatic switch, a relay foreach of said lines for connecting its associated fixed terminals, acommon controlling circuit for said switches normally adapted to controla first one of said switches` means included in said first switch forshifting the control to the other of said switches, and means in saidswitches for controlling said relays.

21. In a trunking system, a pair of lines, each line terminating in ajack, a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit having movable terminals ateach end, xed terminals for each of said lines normally disconnectedtherefrom and accessible to said movable terminals, means for advancingone of said movable terminals into engagement with a fixed terminal ofone of said lines, means for advancing the other of said movableterminals into engagement with a fixed terminal of the other of saidlines, and a relay for each of said lines for connecting its associatedfixed terminals.

22. In a trunking system, a pair of lines, each line terminating in ajack, a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit having movable terminals ateach end, fixed terminals for each of said lines normally disconnectedtherefrom and accessible to said movable terminals, means for advancingone of said movable terminals into engagement with a fixed terminal ofone of said lines, means for advancing the other of said movableterminals into engagement with a fixed terminal of the other of saidlines, and a relay foreach of said lines for connecting its associatedfixed terminals and for disconnecting its associated jack.

23. ln a trunking system, a pair of lines, each line terminating in ajack, a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit havingvmovable terminals ateach end, fixed terminals for eachk of said-lines accessible to saidmovable terminals, means for advancing one of said movable terminalsintoengagement with a fixed terminal of one of said lines, means foradvancing the other of said movable terminals into engagement with afixed terminal of the other of-said lines, each of said means comprisingan automatic switch, and a common controlling circuit for said switches.

24. ln a trunking system, a pair of lines, each line terminating in ajack, a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit having movable terminals ateach end, fixed terminals for each of said lines normally disconnectedtherefrom and accessible to said movable terminals, means for advancingone of said movable terminals into engagement with a fixed terminal of'.one of said lines, means for advancing the other of said movableterminals into engagement with a fixed terminal of the other of saidlines, each of said means comprising an. automatic switch, and a relayfor each of said lines for connecting its associated fixed terminals.

25. In a trunking system, a pair of lines, each line terminating in ajack, a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit having movable terminals ateach end, fixed terminals for each of said lines normally disconnectedtherefrom and accessible to said movable terminals, means for advancingone of said movable terminals into engagement with a fixed terminal ofone of said lines, means for advancing the other of said movableterminals into engagement with a fixed terminal of the other of saidlines, each of said means comprising an automatic switch, and a relayfor each of said lines for connecting its associated fixed terminals andfor disconnecting its associated jack.

26. In a trunking system, a pair of lines, each line terminating in ajack, a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit having movable terminals ateach end, fixed terminals for each of said lines normally disconnectedtherefrom and accessible to said movable terminals, means for advancingone of said movable terminals into engagement with a fixed terminal ofone of said lines, means for advancing the other of said movableterminals into engagement with a fixed terminal of the other of' saidlines, each ofsaid means comprising an automatic switch, a commoncontrollingcircuit for said switches, and a relay for each of said linesfor connecting its associated fixed terminals.

27. In a trunking system, a pair of lines, each line terminating in ajack, a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit having movable terminals ateach end, fixed terminals for each of said llines vnormally disconnectedtherefrom and accessible to said movable terminals, means for advancingone of said movable terminals into engagement with a fixed terminal ofone of said lines, means for advancing the other of said movableterminals into engagement with a fixed terminal of the other of saidlines, each of said means comprising an automatic switch, a commoncontrolling circuit for said switches, and a` relay for each of saidlines for connecting its associated fixed terminals and fordisconnecting its associated jack.

28. In a trunking system, -a pair of lines, each line terminating in ajack, a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit having movable terminals ateach end, fixed terminals for each of said lines accessible to saidmovable terminals, means for advancing one of said movable terminalsinto engagement with a fixed terminal of one of said lines, means foradvancing the other of said movable terminals into engage- .ment with afixed terminal of the other of said lines, each of said means comprisingan automatic switch, a common controlling circuit for said switchesnormally adapted to control a first one of said switches, and meansincluded in said first switch for shiftingthe control to the other ofsaid switches.

29. In a trunking system, a pair of lines, each line terminating in ajack, a cord circuit for interconnecting said lines through switches,

the medium of their associated jacks, a link circuit having movableterminals at each end, fixed terminals for each of said lines normallydisconnected therefrom and accessible to said movable terminals, meansfor advancing one of said movable terminals into engagement with a fixedterminal of one of said lines, means for advancing the other of saidmovable terminals into engagev ment with a fixed terminal of the otherof said lines, each of said means comprising an automatic switch, acommon controlling cirjcuit forsaid switches normally adapted toadvancing one of said movable terminals into engagement with a fixedterminal of one of said lines, means for advancing the other of saidmovable terminalszinto engagement with a fixed terminal of the other ofsaid lines,'each of said means comprising an automatic switch, a commoncontrolling circuit for said switches normally adapted to control afirst one of said switches, means included in said first switch forshifting the control to the other of said switches, and a relay for eachof said lines for connecting its associated fixed terminals and fordisconnecting its associated jack.

3l. In a trunking system, each line terminating in a jack, a cordcircuit for interconnecting said lines through the medium of theirassociated jacks, a link 'circuit having movable terminalsisateach end,fixed terminals for each of said lines normally disconnected therefromand accessible to said movable terminals, means for advancing one ofsaid into engagement with a fixed terminal of one of said lines, meansfor advancing the other of said movable terminals into engagi-linentwith a fixed terminal of the other of said lines, each of said meanscomprising an automatic switch, a common controlling circuit for saidswitches normally adapted to control a first one lof said means includedin said first switch for shifting the controlto the other of saidswitches, a relay fory each of saidlines for connecting its associatedfixed terminals, and means in .said switches for controlling saidrelays.

32. In a trunking system, a pair of lines,

a pair of lines,

'each line terminating in a cuit for interconnecting said lines throughthe medium of their associated jacks, a link circuit having movableterminals at each end, fixed terminals for each of said lines normallydisconnected therefrom and accessible to said movable terminals, meansfor advancing one of said movable terminals into engagement with a fixedterminal of one of said lines, means for advancing the other of saidmovable terminals into engagement with a fixed terminal of the other ofysaid lines, each of said means comprising an automatic switch, a commoncontrolling circuit for said switches normally adapted to control afirst one of said switches, means included in for shifting the controlto the other of said switches, a relay for each of said lines forconnecting its associated fixed terminals and for disconnecting itsassociated Iiack, and means in said switches for controlling saidrelays.

33. In a trunking system,

a pair of lines, each line terminating in a iack, a cord circuit forinterconnecting said lines through the medium of their associated jacks,a link circuit having movable terminals at each end, fixed terminals foreach of-said lines accessible to said movable terminals, means foradvancing one of said movable terminals into engagement'with afixed'terminal of one of said lines. and means for advancing the otherofvsaid movable terminals into engagement with a fixed terminal of theother of said lines, each of said means comprising an automatic switch,a supervisory circuit for said cord circuit and a second supervisorycircuit for said link circuit.

34. In a trunking system', a pair of lines, each line terminating in aliack, a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit having movable terminals ateach end. fixed terminals for each of said lines accessible to saidmovable terminals, means for advancing one of said movable terminalsinto engagement with a fixed terminal of one of said lines, means foradvancing the other of said movable terminals into engagement with afixed terminal of the other of said lines, each of said means comprisingan automatic switch, a supervisory circuit for said cord circuit, asecond supervisory circuit for said link circuit, and a signal commontoboth of said supervisory circuits.

35. ln a trunking system, a pair of lines,

iack. a cord circuit for interconnecting said lines through the mediumof their associated jacks, a link circuit having movable terminals ateach end. fixed terminals for each of said lines accessible to saidmovable terminals, means for advancing lone of said movable terminalsinto engagement with a fixed terminal of one of said lines, means foradvancing the said first switch A other of said movable terminals intoengagement with a fixed terminal of the other of said lines, each ofsaid means comprising an 'automatic switch, a supervisory circuit forcuit for interconnecting said lines through the medium of theirassociated acks, a link circuit having movableterminals at each end,fixed terminals for each of said lines accessible to said movableterminals, means for advancing one of said movable terminals intoengagement with a fixed terminal of one of said lines, means foradvancing the other of said movable terminals into engagement with afixed terminal of the other of said lines, each of said means comprisingan automatic switch, a third line connecting the talkingconductors ofsaid cord circuit with the talking conductors of said link circuit, asignal in bridge of said third line, and a common controlling circuitfor said switches including the two conductors of said third line inparallel.

37. ln a trunking system. a pair of lines, each of which is providedwith normally connected and normally disconnected termi.- nals, a cordcircuit adapted for interconnecting said lines through the medium ofsaid normally connected terminals, a trunk line terminating at each endin an automatic switch. which switches have access to said normallydisconnected terminals. a relay for each of said lines for shifting theline from its normally connected to its normally disconnected terminalsand means included in said switches for operating said relays.

38. ln a trunking svstem, a pair of lines, ea ch of which is providedwith terminals of two kinds, a cord circuit adapted for interconnectingsaid lines through the medium of terminals of one kind. and a trunk lineterminating at each end in an automatic switch. which switches haveaccess to terminals of the other kind.

39. ln a trunking system, a cord circuit and a trunk line inductivelvconnected, and

a pluralitv of lines adapted Jfor interconnection bv either.

40. ln a trunking system. a plurality of lines` a two conductor cordcircuit for yinterconnecting said lines. a two conductor trunk line forinterconnecting said lines, and con-y densers for inductively connectingthe two conductors of the cord circuit, respectively, with the twoconductors of the trunk line.

41'. In a trunking system, a pair of lines, each of which is providedwith normally connected and normally disconnected terminals, a cordcircuit adapted for interconisa necting said lines through the medium of'said normally connected terminals, a trunk means whereby said cordcircuit and Asaid' trunk line are connected in multiple.

42. In a trunking system, a pair of lines, each of which vtwo kinds, acord circuit adapted for interconnecting said lines through the mediumof terminals of one kind, a trunk line terminating at each end in anautomatic switch, which switches have access to terminals of the otherkind, and means whereby said cord circuit and said trunk line areconnected in multiple.

43. In a trunking system, a plurality of lines, a cord circuit forinterconnecting said lines. a pair of automatic switches connected by atrunk line for interconnecting said lines, and means whereby said cordcircuit and said trunk line are connected in multiple.

44;. In a trunking system,a pair oflines, each ofl which is providedwith normally connected and normally disconnected ter-v mlnals, a cordcircuit adapted for interconnecting said lines through the medium ofsaid normally connected terminals, a trunk line terminating at. each endin an automatic switch, which switches have access to said normallydisconnected terminals, a relay for each of said lines for shifting theline from its normally connected vto its normally dis-V connectedterminals, means included in said switches for operating said relays, asupervisory circuit for said cord circuit, a second supervisory circuitfor said trunk line, and a signal common to both of said supervisorycircuits.

45. In a trunking system. a pair of lines,

each of which is provided with terminals'of two kinds, a cord circuitadapted for interconnecting said lines through the medium of terminalsof one kind, a trunk line terminating at each end in an automaticswitch, which switches, have access to terminals of the other kind, asupervisory circuit for said vcord circuit` a second supervisory circuitfor said trunk line, and a signal common to both of said supervisorycircuits.

'46. In a trunking system, a plurality of lines, a cord circuit forinterconnecting said lines, a pair of automatic switches connected b y atrunk line for interconnecting said lines, a supervisory circuit forsaid cord circuit,'a second supervisory circuit for said trunk line, anda signal comm on to both of said` supervisory circuits..

In a trunking system,

each of which isp` provided with normally is provided with terminals off which a pair of lines,

line inductively connected at one end with talking conductors of saidcord circuit and inductively connected at the other end with --talkingconductors of said trunk line, and a common controlling circuit for saidswitches superimposed on said third line.I

48. In a trunking system, a pair of lmes, each of which isprovided withterminals of two kinds, a cord circuit adapted for' interconnecting saidlines through the medlum of terminals of one kind, a trunk line terminating at each end in an automatic switch, which switches have accessto terminals of the other kind, a third line inductively connecting saidcord circuit and said trunk line, and a controlling circuit for saidswitches superimposed on said third line.-

49. In a trunking system, a plurality of lines, a cord circuit forinterconnecting said lines, a pair of automatic switches connected by atrunk line for interconnecting said lines, conductors connecting the twostrandsl of said cord circuit with said trunk line, a signal in bridgeof said conductors, and a controlling circuit for said switchessuperimposed on said conductors.

v50. In a trunking system, a pair of lines, each of which is providedwith terminalsfof two kinds, a cord circuit adapted for interconnectingsaid lines through the medium of terminals of one kind, a trunk lineterminating at each end in an automatic switch` switches have access toterminals of the other kind, a third line'interconnecting said cordcircuit and trunk line, a controlling circuit for said switchessuperimposed onV said third line, and a relay in said controllingcircuit for controlling a first one of said switches.

51. In a trui'iking system, lines,

. a plurality of a ycord circuit for interconnecting said i lines, apair of automatic switches connected by a trunk line for interconnectingsaid lines conductors connecting the .two strands ot said cord circuitwith said trunk line, a controlling circuit for said switches superim-yposed on said conductors, and a relay in said controlling circuit forcontrolling a first one Iof said switches.

52. In a trunking system, a pair oflines, each of which is provided withterminals of two kinds, a cord vcircuit adapted for interconnecting saidlines through the medium V of'terminals of one kind, a trunk line termi-130 nating at-each end in an automatic switch which switches have accessto terminals o the other kind, a third line interconnecting said cordcircuit and said trunk line, a controlling circuit for saidswitchessuperimposed on said third line` a relay in said controlling circuit forcontrolling a first one of said switches, and means included in saidfirst switch for shifting the control of said relay to the other switch.

53. In a trunking system, a plurality of lines, a cord circuit forinterconnecting said lines, a pair of automatic switches connected by atrunk line for interconnecting said lines.

conductors connecting the two strandsA of 15 said cord circuit with saidtrunk line, a controlling circuit for said switches including saidconductors, a relay in said controlling circuit for controllin a firstone of Said switches, and means lncluded in said first 20 switch forshifting the control of said relay to the other switch.

Signed by Ine at Chicago, Cook county, Illinois, this 11th day of March,1916.

EARL R. NEIR. Signed by me at St. Paul, Ramsey county, Minn., this 4thday of March, 1916.

BERNARD C. GROH.

